Mineralogy, Geochemistry, and Thermal Properties of Historic Clay-Bearing Mine Waste Tailings from Tonopah, Nevada: Implications for Reprocessing and Economic Potential

Billions of tons of mine waste are generated globally on an annual basis with a market worth of potentially billions to trillions USD when historic wastes are considered. This study reports the first investigation of clay-dominant mine waste associated with twentieth century mining of an Au–Ag intermediate-sulfidation epithermal system in Tonopah, NV. Sample investigation via SEM–EDS and XRD documented quartz, feldspar, R3 illite–smectite and minor biotite, chlorite, and kaolinite. Trace barite, galena, pyrite, and sphalerite were also identified. Bulk element abundances determined via ICP-MS of sampled wastes are consistent with derivation from the Au–Ag sulfidation system hosted within Tonopah’s Miocene-aged volcanics. Samples were enriched in Ag, As, Au, Cu, Pb, and Zn relative to these volcanics, consistent with trace mineralogy observed and the variable partitioning of some of these elements into galena (PbS), pyrite (FeS2), and sphalerite ((Zn,Fe)S). Relatively low specific surface areas of select samples are consistent with the abundance of quartz and clays, and thus in their current form these wastes are unsuitable for recycling within ceramic production contexts. Recycling these wastes for Ag and Au may be feasible but they are at best low grade. While a toxicity characteristic leaching procedure was not conducted, the presence of potentially toxic elements (e.g., As, Pb) warrants further investigation. Future work which aims to reprocess this regions' mine wastes should therefore evaluate the mobility and (bio)availability of these elements.